Automatic control for aircraft and the like



Feb. 1, 1944. Fl cH L' 2,340,524

AUTOMATIC CONTROL FOR AIRCRAFT AND THE LIKE Original Filed June 2, 1934 Patented Feb. 1, 1944 AUTOMATIC CONTROL FOR AIRCBAF T AND THE LIKE Eduard Fischel, Berlin-Charlottenhurg, and Gerhard Rieper, Berlin-Lichterfeld, Germany; vested in the Allen Property Custodian Continuation of application Serial No. 728,644, June 2, 1934. This application September 15, 1938, Serial No. 230,120.v In Germany July 3.

Claims.

This invention relates to automatic control mechanisms for aircraft and the like, and more particularly to control mechanisms operating by means of a pressure medium such as air, water or oil, and is a continuation of our prior application Serial No. 728,644, flied June 2, 1934.

Mechanisms of the above-mentioned type generally work only periodically or at more or less long intervals; nevertheless, they must continuously be ready for operation. Consequently, it is desirable to geiierate only such a, pressure of the operating fluid or amount of energy as is used actually for the controlling, and in this manner it is possible to attain a substantial reduction in the amount of energy used by the control mechanism.

It is known for the said purposes to make use of one or more airvessels, in which the energy supplied by a pump or any source of power will be stored up during the interval between two control cycles. In connection with these vessels means are provided which will prevent the amount'of stored energy from exceeding a predetermined amount.

It is also known for the above said purposes to furnish the control mechanism with two pumps for feeding the. operating fluid, the one of which is feeding continuously while the other pump will begin to work and cooperate with the first mentioned pump on the arising of a great demand of pressure or energy.

In all these cases the control mechanism will become relatively complicated and voluminous,

in consequence of which it would not be well adapted for automatic control of aircraft and similar purposes.

It is an object of the present invention to provide a comparatively inexpensive and simple device of small weight for effecting an increasing of pressure of the operating fluid on any increase of the demand of pressure or energy, thereby progressively increasing the speed of operation of the controlled member, such as the rudder or other control surface of an aircraft, as the device is moved further from its zero or neutral position. The said device consists of a control valve arranged in such a manner in the output of the pump feeding the operating fluid of the control mechanism, as to secure automatically in. response to needed energy an increase of the pressure, with which the valve disc is pressed on its seat, and consequently the pressure of the operating fluid.

Another object of the invention is to provide means connecting the member to be controlled, such as anaircraft control surface, with the said valve in such a manner jthatthe position of the member or control surface to be controlled will determine the adjustment of the valve and therefore the pressure of the operating fluid, thereby progressively increasing the speed of operation of the controlled member, suchv as therudder or other control surface of an aircraft, as the device is moved further from its zero or neutral position.

Still another object is to provide novel means whereby an automatic pilot will continuously ap ply corrections slowly by actuating the control surface of the aircraft slowly, to keep the craft on a predetermined course and/oron an even keel, and will apply corrections quickly by actuating the control surface at a faster rate when required, to counteract air disturbances such as bumps and gusts.

A further object of. the invention is to provide, in combination with an aircraft having a control surface for controlling the aircraft about an axis, novel means for providing a variable speed of actuation of the control surface such that a minimum speed of actuation is obtained at end near the zero or neutral positionof the servo mechanism and/or control surface and as I the servo mechanism and/or control surface deback to a desired attitude are produced more ram idly than heretofore, and small correction are produced relatively more slowly.

In a fluid pressure operated servo motor of the piston and cylinder type, for example, the foregoing operation; is obtained by increasing the fluid pressure to the servo-motor as the piston moves the control surface further from the zero or neutral position.

For a more complete understanding of the in-- vention reference should behad to the accompanying drawing, in which as an illustrative example the invention isshown in its application to the controlling of a rudder of an aircraft although the invention can also be used for other mounted on the shaft ll.

In the drawing, wherein like reference characters refer to like parts in the several views:

Fig, 1 is a plan view of one form of control mechanism embodying the invention as applied to the control of a rudder of an aircraft shown in dotted lines;

Fig. la is an enlarged sectional view of a servw motor and of a piston valve cooperating therewith;

Fig. 2 shows upon an enlarged scale the control valve of the embodiment according to Fig. 1; and

Fig. 3 is a diagram illustrating the relation between the moment required for the adjusting of the rudder or other control surface and the moment of the control mechanism in dependency on the angular adjustment of the rudder or conadjusted by the control mechanism.

The invention consists substantially in the construction, combination, location and relative arrangement of parts for obtaining the results desired in accordance with the foregoing objects, as will be more fully hereinafter set forth in the specification, as shown in the drawing by way of example, and as finally pointed out in the claims. 1

Referring now to the drawing and more particularly to Fig. 1, the instrument In is shown as a directional device, for example, and serves to measure or to respond to the deviation of the aircraft from a predetermined direction and, as is 7 shown in Fig. 1, it may be a liquid magnetic compass. The magnetic needle I! of the compass carries an electrode I2, movable between two electrodes l3 and I4 fixed to the compass casing l5, which casing is filled with an electrolytic fluid and has a bearing for the pivoted needle I The south direction and retains this direction substantially even when the aircraft swings about bring either the electrode l3 or the electrode H closer to the electrode l2, it being understood that all three electrodes (as well as the compass needle II) are within the casing l5 and in contact with the liquid therein. The compass casing l5 may be rotated about the axis of the needle relatively to the aircraft for changing course, by means of the handle Hi, the shaft l1 and the worm gear N3, the wheel of which is fixed to the compass casing I5 and the worm of which is The course for which the craft has been set can then be read off on the indicator scale l9 driven from said shaft II in any suitable manner as, for example, by worm se rin The above mentionedelectrodes l2, l3 and I I of the compass ID are arranged in an electrical circuit including the said electrodes and conductors leading therefrom, the electrodes l3, M being connected with the terminals of the armature winding 2| of an electromagnet 20, while the electrode I 2 is connected with an alternating current source 22 through the regulating resistor 23, the otherterminal of said source being connected with, an intermediate point of the winding 2|. As will be clear from the drawing, the armature winding 2| of the electromagnet thus consists of two parts forming a differential system with the above said parts of the circuit. In conse quence ofthis, the armature of the magnet will respond only to the difference in the currents flowing through the two parts of its winding and will, for that reason, take the zero position, if the needle ll of the compass I0 is in the middle 'trol surface, or generally of the member to be ascauac position between the two electrodes l3 and I4 flxed to the compass casing l5.

At the beginning of the flight, the crank or handle I6 is operated to turn the compass casing l5 relatively to the aircraft to the position corresponding to the desired course as set with the aid of the indicator I 9. Assuming that the craft is following the intended course, the electrode 2 will be in exactly median position relatively to the electrodes l3 and I4 This will cause exactly equal currents to flow through the two circuits supplied from the source 22. One of these circuits includes the electrode l3, the conductor leading from said electrode to one terminal of the winding 2|. one-half of said winding, and the portion of the electrolyte between the electrodes l2 and I3, together with a portion common to both circuits, viz. the electrode l2, the needlel I, theconductor leading therefrom to the resistance 23, said resistance, the current source 22, and the conductor leading from said source to the intermediate point of the winding 2 I. The other circuit includes, in addition to those common to both circuits, the following parts: the electrode H, the conductor leading therefrom to the other terminal of the winding 2|, the other half of said winding, and the portion of the electrolyte belatter, as-usual, points in the magnetic northtween the electrodes l2 and M. It will be seen that when, as assumed, the electrode I2 is in the median position, that is to say equidistant from the electrodes l3 and H, the resistance of the electrolytic liquid between I 2 and I3 will be exactly the same as that of the liquid between l2 and M. Thus currents of equal strength will flow through the two halves of the winding 2|, and 2 therefore the armature of the magnet 20 will remain in the median position illustrated by Fig. 1. Assuming now that the course of the aircraft is altered in such a direction as to bring the electrode I3 closer to the needle electrode l2 and consequently bring the electrode l4 farther away from said needle electrode ,(this relative position of the three electrodes is indicated in Fig. 1), the result will be that the resistance of the liquid between l2 and i3 is reduced, while at the same time the resistance of the liquid between l2 and I4 is increased. This will increase the current in the branch circuit containing the electrode l2,

and decrease the current in the branch circuit containing the electrode I4. The armature carrying the coil or winding 2| will therefore be deflected in the corresponding direction (clockwise in Fig. 1) Should the course of the craft be altered in theopposite direction, so as to bring the electrode I4 closer to the electrode l2, the armature of the electromagnet 20 will be deflected in the opposite direction (contra-clockwise in Fig. 1).

The armature of the electromagnet 2 0 is coupled by means of a lever 25 and a rod 28 to the one end of a differential lever 21, the other end of which is pivotally connected by means of a rod 28 and a lever 29 to a so-called turn indicator 3|]. The last mentioned instrument measures the angular velocity or rate of turn with which the aircraft deviates from the prede- 21 will accordingly move in response to the devia-' tion of the aircraft from the desired direction and to the angular velocity with which the said deviation takes place.

Motion of the diiferential lever 21 is transmitted by meansof a connecting rod 3i to a lever I! linked at its one end to the said rod 3i and at its middle to a valve stem 33. At its other end the lever 32 is pivotally connected to a piston-rod 34, which carries two pistons 95 and 35 working the hydraulic servomotor is connected to a source of operating fluid, illustrated as a pump 4| driven by a motor,for example an electromotor 42, and feeding out of a reservoir 43 into the said conduit 49. Thefluid discharged by the hydraulic motor 35, 33, 31 passes through a conduit 44 to the said reservoir 43.

Transmission of operating fluid to the hydraulic motor is controlled by a three-part. piston valve 45 flxed to the above said stem 33 and operating in a valve chem-hen to which the conduits 49 and 44 are connected. The last mentioned conduit 44 is connected by a channel 44' to the two outer ports 44 of this chamber 45, while the first named conduit 49 enters the chamber 43 about its middle through a port 49'. The

spectively with the opposite ends of the cylinder 31. In the position illustrated, the piston valve 45 is clear of the ports 43', 43".

So far as the piston rod 34 is connected to the to the above described feeding path for the operating fluid, a second feeding path including:'

the valve 50, the conduit 49 and the reservoir 43 Referring to Fig. 2 showing the valve upon an enlarged scale the valve contains a valve disc 3i carried by stem 52 sliding in a cylindrical guide 53 forming part of a piston 54. This piston is 7 guided at the one end of the valve chamber 55 which chamber is kept tight at the said'end in any known manner. A spring 53 abuts at its one end on the said piston 54 and at its other end by means of a disc 51 on a shoulder on valve stem 52. J

The piston 54 carries at its other end a bearing fork for a roll 59 engaged by a curved disc or cam 59 at its edge. The said curved disc or cam 59 is rotatably mounted at and, as will be clear from'Fig. 1, is connected rigidly with a toothed wheel 5! meshing by means of an intermediate wheel 32 with a toothed wheel 63, the

I shaft of which is coupled (for instance by a belt lever 32 it forms in the well known manner the usual follow-up mechanism to restore the valve to its original position Thus, if for instance the armature carrying the coil 2| is deflected contra-clockwise, the linkage 25, 23, 21, 3!, 32 is shifted to carry the valve stem 33 and the valve 45 downwardly, so that pressure fluid will passv from the conduit 49 through prot 49', the compartment of valve chamber 45 immediately above the middle member of valve 45, port 46' and passage 41 to the lower compartment of cylinder 31. At the same time, the port 44" will be uncovered so that as the pistons 35, 36 move upward, fluid may escape from the upper compartment of cylinder 31 through passage 48, port 46", the compartment of valve chamber 46 immediately belowthe middle member of valve 45, port 44" and channel 44 to the conduit 44. The upward movement of the piston rod 34 will swing the lever 32 clockwise about its left hand end as a temporary fulcrum, and will thus lift the valve stem 33 and the piston-valve 45 back to their original position.

. The novel means of the invention are now provided whereby a variable speed of actuation of the control surface or rudder 39 is obtained such that a minimum speed of actuation is obtained at and near the zero or neutral position of the pistons 33 and 35 and/or rudder 39, and as said pistons and/or rudder depart from the zero or neu-' tral position, thespeed of actuation of said rudder is progressively increased as the departure thereof from neutral increases. For this purpose and to this end there is provided, parallel transmission 34) with the pivot of the control. surface or rudder 39.

The above said curved disc or cam 59 is so shaped that upon rotation of the disc in the clockwise or counterclockwise sense it will move the piston forwards and increase the tension of viation of aircraft from the predetermined direction, the piston valve 45 moves in response to the combined action of the compass Ill and the turn indicator 39. In consequence thereof the pistons 35, 35 of hydraulic motor will move in a well known manner and adjust the control surface'or rudder 39 of the aircraft.

Upon rotation of the control surface or rudder 39 the curved disc or cam 59 also rotates in the manner described above thereby increasing the tension of spring 56. This has the effect that first the amount of operating fluid passing through the valve 59 and theconduit 49 decreases, and simultaneously the pressure and the amount of operating fluid fed into the conduit 49 will increase. As on the other hand the power or moment needed for'adjusting the rudder 39 increases according to the amount of angular deviation of the control surface or rudder from its middle or zero position, the valve 59 will automatically adapt at each time the energy or pressure of operating fluid to the amount or value required momentarily, thereby providing a variable speed of actuation of the control surface or rudder 39, which varies with the amount of displacement of said rudder and/or pistons 35, 33 from the zero or neutral position thereof, and thus providing large corrections more rapidly and small corrections relatively more slowly for bringing the aircraft back to its desired course or attitude.

If the control or'rudder 39 and, therefore. also the curved disc or cam 59 take the zero position, the tension of spring 53 and hence the load of pump 4| will have the smallest value. Inasmuch as at the said zero position the pressure of operor cam 59 in such a manner that the pressure will begin to increase only after a certain deviation of the said disc from zero position. This will also be advantageous in order to avoid disturbing pendulum effects. For a better understanding Fig. 3 showsapproximately in line] the increase of moment for adjustingthe rudder and in line 2 the increase of pressure of the operating fluid bothin dependency on the deviation of the rudder 39 from its zero position. That is to say, in Fig. 3 the abscissae indicate rudder deflections, while the ordinates indicate pressure (with reference to line 2) and moment (with reference to line I). It. has been found advantageous to choose the rate of the smallest pressure P1 to the greatest fluid as 2:5 or greater.

It will be clear from the above description that the new control mechanismwilladapt, in a very simple manner, the value or pressure or energy to the amount required at any time, and will progressively increase the speed of actuation of the pistons, 35, 36 and/or the control surface or rudder 39 as the pistons and/or rudder depart further from their zero or neutral position. As described above the adjustment of the control surface or rudder 39 depends on the combined action of the two instruments l and 30. Therefore, the adjustment of the valve 50 coupled with control surface or rudder 38 will also depend on the combined action of the two instruments I 0 pressure P2 of operating and 30. Hence, itwill be clear that besides the embodiment above described and shown in the drawing, in which embodiment the said instruments act upon the valve 50 by means of the hydraulic motor 35, 36, 31 and the rudder 39, other embodiments of the invention, in which the control instruments act upon the valve 50 in any other way, may be found by those skilled in the art.

whereby the pressure of the operating fluid suppliedto said servo-motor is automatically increased so that the speed of actuation of said control surface is progressively increased as said said craft about an axis, the combination of melns responsive to deviationsof said'craft about said axis, a fluid pressure actuated servo-motor By the term "free load" used in some of the appended claims in connection with the valve 5| is meant that the loading of the valve '(exerted thereon by the spring 56) which tends to close said valve, or to hold it closed, is effected not by moving the valve itself but by simply adjusting (by means of the curved disc or cam 59) the pressure by which the valve is urged in the closing direction, independently of the position of the valve relatively to its seat.

While the invention has been illustrated and described as embodied in a particular concrete form, itshould be understood that the invention is not limited thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of the invention, the scope of which is set forth in the annexed claims.

What is claimed is:

1. In an automatic control for aircraft and the like having a control surface for controlling the craft about an axis, the combination of means responsive to deviations of said craft about said axis, a fluid pressure actuated servo-motor connected to said control surface for actuating the same, means for continuously supplying a fluid operating medium to said servo-motor, means actuated by said deviation responsive means for controlling the flow of said fluid medium to said servo-motor to actuate the latter, means comprising a yieldingly loaded valve exposed to the pressure of said fluid medium and determining the pressure thereof, and means responsive to the position of said control surface for effecting an adjustment of the free load on said valve.

connected to said control surface for actuating the same, means for continuously supplying a fluid operating medium to said servo-motor, means actuated by said deviation responsive means for controlling the flow of said fluid medium to said servo-motor to actuate the latter, means providing a branch line for diverting a portion of said fluid medium, a valve controlling said branch line and exposed on one side to the pressure of said fluid medium, a spring urging said valve in opposition to said pressure, and means responsive to the position of said control surface for adjusting the free load on said spring and thereby adjusting the amount of fluid medium diverted and the pressure of the fluid me- ,dium continuously delivered to said servo-motor operatively with said rudder, a pump having a delivery connection for continuously supplying a fluid operating medium to said servo-motor, a yielding valve exposed to the delivery pressure of said pump and loaded to Oppose said pressure and determine the, magnitude thereof, and

'means responsive to the position of said rudder to effect an adjustment of' the free load on the valve and thereby automatically adjust the pressure of the continuously supplied operating fluid to the working requirements so that the rate of movement of the rudder is progressively increased as it moves further from its neutral position.

4. In an automatic pilot, the combination of a compass, a rudder, means comprising a servomotor connecting the compass operatively with said rudder, a pump having a delivery connection for continuously supplying a fluid operating medium to said servo-motor, means providing a by-pass connected with the delivery side of the pump, a valve controlling said by-pass and exposed on one side to the delivery pressure of said pump, a spring urging said valve in opposition to said pressure, and means responsive to the position of said rudder to adjust the free loading of said spring and thereby adjust the amount of the fluid by-passed and the pressure'ofthe to the required variation in pressure for the range of movement of said rudder, so that the rate of movement ofsaid rudder is varied as it moves from its neutral position.

7. An automatic pilot, the combination of a compass, a rudder, a servo-motor connecting the compass operatively with said rudder, means for continuously supplying a fluid operating medium to said servo-motor, a yielding loaded valve exposed to the pressure of said fluid medium and determining the pressure thereof, means for applying to said valve a tree load opposing the pressure exerted by said fluid medium on said valve, an element movable to effect an adjustment of the tree load on said valve, and an operative connection responsive tochanges in the position of said rudder to move said element whenever there is a change in such position and thereby automatically adjust the pressure of the continuously supplied operating fluid to the working requirements so that the rate of movement of said rudder is progressively increased as it moves further from its neutral position.

8. In an automatic pilot, the combination of a directional device, a rudder, means comprising a servo-motor connecting th directional device operatively with said rudder, means for continthe continuously supplied operating fluid .to the working requirements so that the rate of movement of said rudder is' progressively increased as it moves further irom its neutral position.

9. In an automatic pilot, the combination of a directional device, a rudder, means comprising a servo-motor connecting the directional device operatively with said rudder, means for continuously supplying a fluid operating medium to said servo-motor, a yielding loaded valve exposed to the pressure of said fluid medium and determining the pressure thereof, an element movable to eflect anadjustment of the free loadon said valve, and means providing an operative connection between the rudder and said element to move the latter whenever there is a change in the position of said rudder, thereby automatically to adjust the pressure of the continuously supplied operating fluid to the working requirements so that the rate 01 movement of the rudder is progressively increased as it moves further from its neutral position.

10. In an automatic pilot, the combination of a rudder, a servo-motor for operating said rudder, means for continuously supplying a fluid operating medium to said servo-motor, a directional device for controlling said servomotor, a yielding loaded valve exposed to the pressure of said fluid medium continuously supplied to said servo-motor, an element movable independently of said fluid-supplying means to efl'ect an adjustment oi. the free load on said valve, and

means providing an operative connection responsive to changes in the position of said rudder to move said element whenever there is a change in such position and thereby automatically adjust the pressure of the continuously upplied operating fluid to the working requirements so that the rate of movement of the rudder is progressively increased as it moves further from its neutral position.

EDUARD FISCHEL. GERHARD RIEPER. 

